Generally, the present invention relates to spinal implant devices, surgical tools and associated techniques for promoting spinal fusion.
It is known that when an intervertebral disc degenerates or is damaged, there is often a compression of the disc and a reduction in the normal intervertebral height. Typically, this condition results in abnormal motions that become a source of pain.
In order to treat pathologies of this type, the disc is often stabilized to eliminate the abnormal motions caused by disc disorders or injuries. Generally, one approach is to prevent articulation between the two vertebrae situated on each side of the damaged disc by bone fusion. This fusion fixes the vertebrae to each other, eliminating the relative mobility causing the pain. Various spinal implants to promote fusion between adjacent vertebrae have been proposed. It has been proposed to interconnect the two vertebrae by a kind of rigid U-shaped stirrup, which restores the discal height with a bone graft material disposed inside the stirrup. However, one drawback of this proposal is its diminishing effectiveness over a period of time.
Another proposal for promoting spinal fusion includes implanting a spinal cage to interconnect the adjacent vertebrae; the spinal cage includes a cylindrical member provided with a series of openings and provided with anchoring points. This implant is placed in a recess formed in the intervertebral disc and penetrates the opposite cortical endplates of the two vertebrae, which were previously hollowed out to receive the implant. This penetration forms openings in the sub-chondral endplates to place spongy bone of the vertebrae in contact with bone graft material placed inside the implant, facilitating bone fusion. U.S. Pat. No. 5,015,247 provides one example of this approach.
Yet another proposal for spinal fusion comprises inserting hollow tubular implants having a generally ovoidal external shape into the intervertebral space. However, these implants require both annular ribs to inhibit axial displacement and longitudinal ribs or teeth to prevent rotation of the implant about its longitudinal axis. One example of this approach is found in U.S. Pat. No. 5,683,463 issued to Godefroy et al. In another example in U.S. Pat. No. 5,888,224 issued to Beckers et al., a rotatable implant for spinal fusion is disclosed. The rotatable implant requires a linking connector to inhibit longitudinal rotation. Other rotatable implants are described in U.S. Pat. No. 5,607,424 issued to Tropiano.
However, one drawback of these proposed implants is their lack of support of the cortical bone tissue, particularly bearing against the peripheral wall of the vertebral bodies. This contributes to their diminishing effectiveness in maintaining normal disc height over a period of time.
Proper performance of a spinal implant of this type requires balancing the need to promote fusion between the spongy bone and the need to form a reliable load bearing relationship with the stronger cortical bone. As a result, the spinal implant must be neither engaged too far into the openings provided in the cortical endplates to provide a sufficiently dense load bearing surface, nor insufficiently inserted, in which case the bone fusion between the two vertebrae would be adversely affected by a poor anchorage. Thus, there is a demand for devices and techniques that facilitate attaining the proper balance between fusion and load support.
Thus, in light of the above described problems, there is a continuing need for advancements in the treatment of spinal deformities, including improved spinal implants and devices relating to spinal fusion and for surgical methods to treat spinal deformities. The present invention is such an advancement and provides a wide variety of benefits and advantages.
The present invention relates to spinal implants, surgical tools and the use thereof. Various aspects of the invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms and features, which are characteristic of the preferred embodiments disclosed herein, are described briefly as follows.
According to one form of the invention, the spinal implant comprises a body having a central part arranged to allow arthrodesis and at least one terminal part for bearing against the cortical bone of the vertebral endplates. The central part is adapted to penetrate the vertebral endplates, transversely projecting from the terminal bearing part. Thus the invention achieves a separation between the end parts constituting the load bearers, and the intermediate part of the implant which permits fusion. In addition, the central part may include at least one cavity for receiving a bone graft material.
In another form of the present invention, an implant for insertion between a first vertebra having a first cortical bone endplate and a second vertebra having a second cortical bone endplate includes two terminal parts. The first terminal part defines a first bearing surface to bear against the first cortical bone endplate and a second bearing surface opposite the first surface to bear against the second cortical bone endplate. The second terminal part opposes the first terminal part and defines a third bearing surface to bear against the first cortical bone endplate and a fourth bearing surface opposite the third surface to bear against the second cortical bone endplate. The implant has an elongated central part defining an upper projection extending past the first and third surfaces, and a lower projection extending past the second and fourth surfaces. These projections correspondingly pass through openings in the first and second cortical bone endplates when the first and third surfaces bear against the first cortical bone endplate and the second and fourth surfaces bear against the second cortical bone endplate. The terminal parts are dimensioned to facilitate restoration of the natural geometry of the intervertebral space (lordosis, kyphosis, and parallel discs). Thus, the first and second surfaces may be separated by a first distance, and the third and fourth surface may be separated by a second distance greater than the first distance to accommodate a natural curvature of the spine.
In a further form of the present invention, an implant with two terminal parts also has an elongated central part that includes a pair of longitudinal walls defining a cavity. The walls defme a first edge projecting past the first and third surfaces and a second edge projecting past the second and fourth surfaces. The first and second edges correspondingly penetrate the first and second cortical bone endplates when the first and third surfaces bear against the first cortical bone endplate and the second and fourth surfaces bear against the second cortical bone endplate.
According to another form, the bearing surfaces of the terminal end parts are defined by flanges extending from opposing ends of the implant along its longitudinal axis. Preferably, the bearing surfaces are generally flat for bearing against the cortical bone of the vertebral endplates of the two adjacent vertebrae. It is also preferred that openings be cut into the cortical endplates in their central regions corresponding to the length of a central part of the implant along the longitudinal axis and leaving a region of the cortical bone endplates around the periphery of the openings. The length of the remaining peripheral endplate corresponds to the length of the bearing surfaces along the longitudinal axis. When the implant is placed in position, the edges of the walls of the central part engage the openings cut in the cortical endplates and consequently do not substantially bear against the remaining peripheral portion of the endplates. A cavity may be defined by the central part that holds bone graft material in contact with the spongy bone of the two vertebrae. In contrast, the bearing surfaces of the flanges are disposed adjacent the edges of the openings of the cortical endplates and bear against the remaining portions of the endplates to establish a strong load-bearing relationship. Thus, both bone fusion and support are distinctly accommodated by different parts of the implant structure, which permits obtaining a satisfactory support of the vertebral bodies on the implant and an excellent arthrodesis.
Yet another form of the present invention includes a cutting tool accessory to prepare the cortical endplates of two adjacent vertebrae for insertion of an implant. This tool comprises a proximal handle connected to an elongated shaft configured to rotate about a longitudinal axis of the tool. The tool also includes a first non-cutting portion with the shaft extending therethrough and being configured to rotate relative thereto. A cutting portion is fixed to the shaft to rotate therewith and is positioned distal to the first non-cutting portion. The cutting portion includes a first pair of generally parallel opposing faces and a second pair of opposing faces each extending between the first pair of faces. The second pair of faces each defines a number of cutting teeth. A second non-cutting portion is fixed to the cutting portion that includes a distal head. The first non-cutting portion, the cutting portion, and the second noncutting portion have a rotatably selectable alignment that presents a generally constant height corresponding to the intervertebral space defined between the cortical bone endplates to facilitate insertion therein. Once inserted, the cutting portion may be rotated out of this alignment to cut a first opening in the first cortical bone endplate and a second opening into the second cortical bone endplate. The cutting portion and the non-cutting portions may be arranged to provide uniform, symmetrical cutting of these openings with a predetermined length corresponding to the dimensions of a given implant device.
In an additional form, a technique of spinal fixation includes cutting adjacent vertebrae and inserting an implant therebetween to promote fusion and provide suitable support. The implant may be inserted by anterior or posterior surgical approaches. The cutting may be performed by the cutting tool of the present invention and may include initially inserting the tool so that a first pair of faces are in contact with a respective one of the first and second cortical bone endplates, turning a handle to rotate the cutting portion to remove cortical bone with cutting teeth defined by a second pair of faces, and withdrawing the tool. The tool may be used to form openings readily positioned in the central region of the adjacent vertebrae leaving a portion of the cortical bone endplates about the openings. The insertion of the implant may include positioning the implant of the present invention between the first and second vertebrae and turning the implant about one quarter of a turn.
In another form of the present invention, there is provided an implant for insertion between a first and a second vertebrae, each vertebra having a cortical bone endplate surface. The implant includes a first terminal part that defines a first bearing surface substantially planar and adapted to bear against a first cortical endplate surface and an opposite second bearing surface substantially planar and adapted to bear against a second cortical bone endplate surface; a second terminal part opposite the first terminal part, wherein the second terminal part defines a third bearing surface adapted to bear against the first cortical bone endplate surface and a fourth bearing surface adapted to bear against the second cortical bone endplate surface; and an elongated body extending from the first terminal part to the second terminal part. The implant has an elongated central part that defines a longitudinal axis and has an upper surface arcuate along the longitudinal axis and a lower surface arcuate along the longitudinal axis. In preferred embodiments, the implant includes a cavity for receiving bone osteogenic material to promote bone fusion between adjacent vertebrae. The implant also includes antiexpulsion features such as, for example, at least one ridge transverse to the longitudinal axis. Preferably the implant includes a plurality of ridges proximate to the first and second bearing surfaces to inhibit expulsion of the implant. Furthermore, the second terminal part can be curved to facilitate insertion of the implant into the prepared intervertebral space.
In another form the present invention provides an implant for insertion between a first vertebra and a second vertebra, where the first vertebra has a generally vertically extending first peripheral wall and a first cortical bone endplate and the second vertebra has a generally vertically extending second peripheral wall and a second cortical bone endplate. The implant comprises: A first terminal part defining a first bearing surface adapted to bear against a portion of the cortical bone endplate proximate to the first peripheral wall and an opposite second bearing surface adapted to bear against a portion of the second cortical bone endplate proximate to the second peripheral wall; an elongated body extending from said first terminal part, the body defining a longitudinal axis and having an upper surface and a lower surface, wherein the first upper surface and the second lower surface are arcuate along the longitudinal axis; and a second terminal part opposite the first terminal part and having a insertion face extending from the upper surface to the lower surface wherein the insertion face is provided to ease insertion of the implant between the first vertebra and the second vertebra.
In yet another form of the present invention, there is provided a tool for insertion between a first vertebra having a cortical bone endplate and a second vertebra having a second cortical bone endplate. The insertion tool includes a proximal handle connected to an elongated shaft configured to rotate about a longitudinal axis of the tool; an outer sleeve adjacent to the handle and the shaft extending through the sleeve and configured to rotate relative thereto; a cutting portion fixed to the shaft to rotate therewith, the cutting portion including a pair of generally parallel opposing arms, each arm having a first arcuate cutting edge and an opposite second arcuate cutting edge; and a non-cutting portion fixed to the cutting portion and distal to the handle, wherein the non-cutting portion is configured to align the cutting portion between the first cortical bone endplate of the first vertebra and the second cortical bone endplate of the second vertebra. The insertion tool also can include a stop adapted to bear against the first or second vertebra to limit the depth of insertion of the tool within the intervertebral space. The tool preferably includes a cavity provided between the first and second arms of the cutting portion. The cavity provides a receptacle for receipt of bone debris generated during the scraping procedure. The cutting portion and the non-cutting portion of the tool are adapted to position first and second cutting edges between the first and second vertebrae such that rotation of the cutting head removes substantially equal amounts of bone from the first and second endplates of the adjacent vertebrae.
One object of the present invention is to provide a spinal implant device to promote fusion between adjacent vertebrae. Further objects, features, aspects, forms, advantages and benefits shall become apparent from the description and drawings contained herein.